1. Field of the Invention
The present invention relates to communication systems, in particular to a system that provides the capability to alter communication characteristics of a communication link between modems in a telecommunication system.
2. Description of the Related Art
A typical telecommunication system operates with at least two modems that communicate across a communication link that is established through a telephone network. The communication link has communication characteristics that are established when one modem begins to communicate with another modem across the communication link. These communication characteristics typically include one or more communication channels for exchanging data across the communication link and a second communication channel through which no data is exchanged but a xe2x80x9cguard tonexe2x80x9d is included that prevents communication signals from undesirably interfering with each other.
In a modem day Public Switched Telephone Network (PSTN), the transport of a modem signal is digital and does not exhibit the same range of impairments as an older analog/FDM switch network. For example, the presence of noise, phase jitter, frequency offset and gain hits are significantly reduced in the digital PSTN. V.34 was developed in consideration of the improved GSTN infrastructure and relies upon PSTN to achieve the high data rates that are supported. However, V.34 half-duplex (V.34HDX) has some performance limitations if it is connected over the older analog/FDM switch network. For example, in the case of facsimile transmissions, the reliability of the passing facsimile images could be impaired if V.34HDX operates across an older analog/FDM switch network.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.
Various aspects of the present invention may be realized through a communication system that includes a first modem and a second modem that establishes a communication link between the first modem and the second modem. The communication link has a first set of communication characteristics including a first communication channel or group of communication channels through which at least data is exchanged and a second communication channel through which no data is exchanged. Either the first modem or the second modem is configured to signal for a change, via the second communication channel, in the first set of communication characteristics.
The first modem of the communication system is often configured to signal for a change in the first set of communication characteristics via the second communication channel and the second modem is often configured to dismiss the signal from the first modem on the second communication channel. In this embodiment, the first modem is typically configured to recognize that the signal on the second communication channel has been dismissed by the second modem and the first modem refrains from further signaling to the second modem via the second communication channel. In another embodiment, the first modem is configured to signal for a change in the first set of communication characteristics via the second communication channel and the second modem is configured to recognize and respond to the signal. The first modem commonly includes transition processing circuitry that monitors the first set of communication characteristics between the first and second modems, that indicates when communications via the communication link may be improved by shifting to a second set of communication characteristics on the communication link, and that enables a shift in the communication link to the second set of communication characteristics. The second set of communication characteristics may include at least a reduced data transmission rate, at least an increased data transmission rate, or even at least a data transmission rate that is similar to a data transmission rate of the first set of communication characteristics.
Various aspects of the present invention may also be realized in a method for a communication system having a communication link between a first communication device and a second communication device to inquire whether a first set of communication characteristics in the communication link may be modified. In one embodiment, the method comprises establishing at least first and second communication channels across the communication link, the first communication channel exchanging at least data according to the first set of communication characteristics, the second communication channel exchanging no data. The method also includes inquiring, by the first communication device across the second communication channel, whether the second communication device recognizes communications across the second communication channel.
Inquiring whether the second communication device recognizes communications across the second communication channel often comprises passing communication signals across the second communication channel in such manner that the communication signals do not interfere with communications on the first communication channel. The method may also comprise determining, by the first communication device, that communication signals are not recognized across the second communication channel by the second communication device. In addition, the method may also comprise discontinuing further inquiries across the second communication channel from the first communication device. On the other hand, the second communication device may acknowledge, across the second communication channel, that communication signals are recognized across the second communication channel. In this aspect, the method often comprises monitoring the first communication channel to analyze whether the first set of communication characteristics of the first communication channel should be modified.
In some embodiments, the method further comprises determining that the first set of communication characteristics of the first communication channel should be modified and a new set of communication characteristics should be established. Either the first or second communication device indicates, across the second communication channel, that the first set of communication characteristics should be replaced with the new set of communication characteristics, and the first set of communication characteristics are replaced with the new set of communication characteristics without interfering with communications between the first and second communication devices.
Various aspects of the present invention may also be found in a communication system comprising a source communication device, a destination communication device, and a communication link having a first set of communication characteristics for electronic communications between the source communication device and the destination communication device. The source communication device includes circuitry that generates a request signal to establish at least one communication channel with the destination communication device across the communication link. The destination communication device includes circuitry that receives and acknowledges the request signal from the source communication device and that completes establishment of the at least one communication channel. The destination communication device also includes an indicator that indicates to the source communication device that the first set of communication characteristics in the communication link should be modified and a second set of communication characteristics should be established.
In certain embodiments, the indicator of the destination communication device comprises circuitry that generates an indication signal that is transparent to data communications across the communication link. Further, the source communication device may include additional circuitry that acknowledges receipt of an indication signal from the destination communication device, the indication signal being received across a second communication channel that does not pass data between the source and destination communication devices. The indicator of the destination communication device may include circuitry that amplitude modulates a guard tone with a second frequency and depth that is dependent upon requirements of the first set of communication characteristics on the communication link. In addition, the indicator of the destination communication device may indicate to the source communication device that data communications across the communications link that utilize the first set of communication characteristics could be improved by shifting to a second set of communication characteristics.
Other aspects of the present invention will become apparent with further reference to the drawings and specification which follow.